This invention relates to exhaust filters for vacuum cleaners. In particular, this invention relates to a multistage vacuum cleaner exhaust filter in which one of the stages ionizes the exhaust air.
A typical vacuum cleaner, whether of the canister or upright type (with the exception of upright vacuum cleaners of the external bag type), has a body or housing enclosing a compartment for the collection of dirt. An air-flow path is provided through the housing from a suction port to an exhaust port. A motor/fan unit creates a partial vacuum that draws dirt-laden air in through the suction port to the dirt collection chamber. The air then passes through a filter, which typically, but not necessarily, is in the form of a bag made from filter paper, which traps the dirt and allows "clean" air to pass. This "clean" air exits through the exhaust port.
It is well known that the "clean" air exiting a vacuum cleaner exhaust port is not, in fact, clean. Because the filtering properties of the filter bag or other dirt collection filter are selected to allow for a reasonable pressure drop, fine particles of dust and dirt may pass through the filter and out the exhaust port. It is therefore known to provide a further filter on the exhaust port to capture at least some of those fine particles. While the main filter must be cleaned or, in the more common case of a filter bag, emptied or disposed of, relatively often, the exhaust filter typically is cleaned less often.
Although the filter bag is emptied or disposed of relatively frequently compared to the exhaust filter, dirt may remain in the filter bag for a considerable time before it is disposed of. Odors may be generated by bacteria or fungi on the dust particles captured in the filter bag. Moreover, even with an exhaust filter, a certain amount of fine particulates may nevertheless escape into the room air.
Therefore, it would be desirable to be able to provide a vacuum cleaner exhaust filter which is finer than previously known exhaust filters to reduce the amount of fine particulates that escape in the exhaust air, and which reduces odors and even improves room air quality.